Characteristics of nystagmus and illusion evoked by optokinetic stimuli

To study the characteristics of human psychophysiological responses to optokinetic stimulus, 30 male medical students were given a series of optokinetic step stimulus (5, 10, 15, 20, 30, 40, 60, 80, 100, 120 deg/sec ) (clockwise). Each stimulus lasted for 20 seconds. Optokinetic nystagmus was recorded on tape. At the same time, the latency and estimated fuzzy magnitude of the illusion were noted down. The nystagmus was analysed with a computer system of ENG and the magnitude of illusion was measured with a fuzzy set model. The results were: 1. Both the slow velocity (SV) and fast velocity (FV) of optokinetic nystagmus increased as stimulus speeded up and reached their peaks at 60 deg/sec, which remained constant from 60 to 120 deg/sec; 2. From 5 to 120 deg/sec, the magnitude of optokinetic illusion increased linearly as stimulus speeded up. Optokinetic illusion and optokinetic nystagmus are human psychophysiological responses to the same optokinetic stimulus, they are different in trend of change, and when optokinetic stimulus is at 60-l20 deg/sec, illusion response is more stable than nystagmus response.